1.什么是皮肤屏障？
皮肤是我们抵御外部环境的第一道屏障。这种复杂的屏障可以保护身体免受各种攻击： 化学攻击，有毒物质或过敏原，物理攻击，可以是机械的或例如与 紫外线辐射 （导致皮肤老化）以及微生物攻击，即细菌、病毒或真菌的攻击。
The structure and properties of our skin such as its thickness, transcutaneous water loss or sebum secretion vary from one area of the body to another. 在其各层中，角质层或角质层是皮肤的最外层，起着基础作用。
2.它的作用是什么？
我们的皮肤屏障假设 四大主要功能 ：物理、化学、微生物和免疫防护。 These four functions interact to ensure stability, hydration, avoid imbalances in the skin microbiome and reduce inflammatory reactions of the skin.
物理保护
这种保护主要由第一层皮肤提供，称为 角质层。这确保了皮肤的紧致性并限制经皮水分流失。 It is composed of dead cells (corneocytes) linked together by specialized proteins (fillagrin, corneodesmosomes, tight junctions) and lipids (fatty acids, cholesterol, ceramides) which form an intercellular cement.该系统使皮肤防水并且不易被病原微生物（细菌、病毒或真菌）渗透。
化学防护
The chemical protection of the skin is composed in particular of lipids (such as sebum) and natural hydration factors, which make it possible to maintain an acidic pH between 4 and 6. This acidity slows the development of harmful bacteria while promoting enzymatic processes in the skin such as cornification (cell renewal mechanism), the elimination of dead cells and the synthesis of lipids. Keratinocytes also secrete antimicrobial peptides (defensins, cathelicidins) which prevent the growth of unwanted bacteria and germs and activate the skin's immune defense.
微生物防护
我们的皮肤是微生物（细菌、真菌、病毒）的家园，它们与皮肤和谐相处。它们与皮肤屏障的相互作用形成了针对攻击的额外防御。 From birth, the skin is colonized by microorganisms which evolve over time, with notable changes during puberty under the effect of hormones and increased sebum production. 这个微生物组 actively participates in the protection of our body by preventing harmful micro-organisms from developing thanks in particular to maintaining the acidic pH.它还可以刺激皮肤的免疫系统。
免疫保护
最后，皮肤具有内置的免疫系统。免疫细胞与微生物组相互作用，检测外部威胁并激活免疫反应。 This system is composed of resident cells (Langherans cells, dendritic cells) which provide innate (rapid reaction to intruders) and adaptive (more specific response) immunity.因此，皮肤根据威胁做出反应和适应，同时保持平衡。
要点：
皮肤屏障在保护我们免受外部侵害和维持体内水分方面发挥着重要作用。它基于四个主要作用：物理屏障（角质层和脂质）、化学屏障（酸性 pH 值和抗菌肽）、微生物屏障（皮肤微生物组）和免疫屏障（朗格汉斯细胞和免疫细胞）。这些作用共同使我们的皮肤成为一个卓越的防御器官，保持其完整性对于最佳皮肤健康至关重要。
